1. Field of the Invention
The present invention generally relates to a lithography system and, more particularly, to a simplified reticle stage removal system for an electron beam system.
2. Background Description
Lithographic processes are typically used to manufacture memory, logic and other types of semiconductor devices. In one type of lithographic process, a medium such as light or non-visible radiation (e.g., DUV or a charged particle beam) is projected through a reticle (or mask) to pattern a resist on a wafer to allow selective processing. In most conventional systems, the reticle is positioned by a stage which supports the reticle.
Accurately positioning the reticle is important in the semiconductor fabrication process. This accurate positioning allows the desired pattern to be transferred from the reticle to the wafer. This pattern may be, for example, used to fabricate an array of many electric devices. Conventional reticle stages provide relatively precise motion in the X-axis and Y-axis directions, and sometimes slight motion in the vertical (Z-axis) direction. A reticle stage is generally used when the reticle is scanned to facilitate compensation of aberration. Conventional stages attempt, with varying degrees of success, to provide as smooth and precise scanning motion as possible, and accurate reticle to wafer alignment. Conventional systems currently have positional resolution capabilities of about 40 nm, which may be more limited than desired.
The reticle stage has typically been two dimensional. For instance, two-dimensional stages have been developed in which force generating elements of the stage assembly are supported by a reaction frame independent from the electron beam or optical column and from the weight of the reticle stage plate. (See, U.S. Pat. No. 6,130,490 to Lee). Also, reticle stage technology has developed based on the recognition that the guide structure that was located directly under the reticle stage, in early reticle stage designs, interferes with directing light or an e-beam, and may cause degradation of position resolution and a source of transmitted vibration through the reticle and through the stage to the underlying projection lens. Hence, efforts began to remove the guides and so-called xe2x80x9cguideless reticle stagesxe2x80x9d have been developed. It is further noted that a third degree of reticle stage technology has been proposed. (See, U.S. Pat. No. 6,147,421, to Takita et al.) In this type of system, a platform is positionable in at least three degrees of freedom by using a system of multiple magnets and multiple coils.
Additional features also merit attention when designing a reticle stage and other sub systems of the lithography system. For example, throughput in a lithography system is a feature of interest, as is accuracy to support economy of manufacture as well as quality and high manufacturing yield. Additionally, some conventional reticle stages suffer from a problem that external forces and/or small reaction forces adversely affect the performance of the stage; namely, forces can cause vibration and body distortion which highly affect the tracking error of the stage. Meanwhile, another feature to consider in a reticle stage is maximizing servo bandwidth because this results in faster response to correct and reduce errors caused by disturbances from the ideal position and velocity. Also, avoiding distortion to the stage base and frame is also an important consideration because such distortion may not be directly measurable by the metrology system (laser interferometers) and can result in an uncompensated error.
Another desirable feature of lithography systems is the periodic access and removal of the reticle stage for maintenance such as cleaning, replacement and the like. This is very important due to the fact that the reticle is subject to heating, high currents and other erosive factors within the vacuum chamber. These many environmental factors such as vibrations and body distortions subject the reticle stage as well as reticle table to misalignments and other accuracy considerations. However, current lithography systems provided for relatively cumbersome and complex removal of the reticle stage. These systems also do not provide and easy access to the reticle stage. By way of illustration, FIG. 1 shows a highly schematic view of a conventional lithography system with a cumbersome and complex removal system. In the system shown in FIG. 1, a reticle table (RT) is mounted to a reticle stage (RS) and is positionable between the projection optics (PO) and illuminator optic (IO). The conventional chamber parting line, designated as xe2x80x9cpxe2x80x9d, is representative of a split of the vacuum chamber.
In order to remove the reticle stage in the system of FIG. 1, the reticle stage must be removed in the removal direction of Dir0, perpendicular to the plane of the reticle table. However, to accomplish this removal, the illuminator optics (IO) and the entire upper casing of the lithography system must be disassembled. This is mainly due to the fact that the illuminator optics, due to the design of current systems, is supported by the upper casing of the lithography system. Then, to reinstall the reticle stage, the illuminator optics and the entire upper casing or part of the lithography system must be reassembled and realigned after the reticle stage is installed into the system. This procedure is complex and costly. It also requires a substantial amount of down time of the lithography system, which could otherwise be used for the further fabrication of semiconductor devices. Also, such a removal system requires a realignment of the reticle stage as well as the illuminator optics and other subsystems, all very costly and time consuming procedures. Additionally, there is no convenient access to the reticle stage for periodic maintenance or other minor repairs or adjustments. In summary, the above difficulties present a trade-off between maintenance and throughput such that both lithographic exposure and economy are adversely affected.
In a first aspect of the invention, a lithography system has a reticle chamber having a reticle chamber opening. A reticle chamber maintenance panel is removably mounted to the reticle chamber opening. The reticle chamber maintenance panel may be pivotably mounted to the chamber and the opening may be at an angle such as, for example, between 0xc2x0 and 45xc2x0, or other such angle. A reticle stage is housed within the reticle chamber and is substantially completely accessible and removable through the reticle chamber opening. In embodiments, the reticle stage is removable from the reticle chamber in a first direction which is in a plane substantially horizontal to a reticle table mounted to the reticle stage. In further embodiments, a projection optic system and an illuminator optic system are mounted to the body structure, and do not have to be removed or disassembled when the reticle stage is accessed or removed. The reticle chamber opening provides access to substantially a center of gravity of the reticle stage.
In still another aspect of the present invention, the lithography system includes a reticle chamber having a reticle chamber angled opening and a reticle chamber maintenance panel which is removably mounted to the reticle chamber angled opening. An optical system for illuminating and projecting a source on a reticle is also provided. A reticle stage having a reticle table is positioned within the reticle chamber. The reticle table may be positioned between components of the optical system. In embodiments of this aspect, the reticle chamber angled opening provides access to substantially a center of gravity of the reticle stage, and permits removal of the reticle stage without removing the optical system. The reticle stage may be removable from the reticle chamber via the reticle chamber angled opening in a first direction which is in a plane substantially horizontal to the reticle table.